Access TTree in Python using PyROOT and fill a histogram¶

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First import the ROOT Python module.

In [1]:

import ROOT

Welcome to JupyROOT 6.07/07

Optional: activate the JavaScript visualisation to produce interactive plots.

In [2]:

%jsroot on

Open a file which is located on the web. No type is to be specified for "f".

In [3]:

f = ROOT.TFile.Open("https://root.cern.ch/files/summer_student_tutorial_tracks.root");

Loop over the TTree called "events" in the file. It is accessed with the dot operator. Same holds for the access to the branches: no need to set them up - they are just accessed by name, again with the dot operator.

In [4]:

h = ROOT.TH1F("TracksPt","Tracks;Pt [GeV/c];#",128,0,64)
for event in f.events:
    for track in event.tracks:
        h.Fill(track.Pt())
c = ROOT.TCanvas()
h.Draw()
c.Draw()